The present invention relates to a thermal transfer recording medium comprising a foundation having a heat-meltable ink layer on one side thereof and a back layer on the other side thereof.
A conventional thermal transfer recording medium of this type is adapted to form printed images by superimposing a receptor on the side of the heat-meltable ink layer and heating the recording medium from the back side thereof by means of a thermal head to transfer the heat-meltable ink onto the receptor.
The main purpose of providing the back layer is to prevent the so-called sticking phenomenon wherein the foundation melts and sticks to the thermal head.
Such a back layer is composed of a heat-resistant resin as a main ingredient. For instance, a back layer is known which is formed by applying onto a foundation a silicone-modified resin such as a silicone-modified acrylic resin, followed by curing.
When a thermal transfer recording medium having the back layer made of the silicone-modified resin is employed to form printed images, there is a disadvantage that the heat-meltable ink at the heated portion is not completely transferred onto a receptor, resulting in printed images having dropout portions or voids.
The present inventor's investigation of the causes reveals the following: With a thermal transfer recording medium which is wound in the form of a roll, the heat-meltable ink layer and the back layer are in contact with each other. In such a state, a low molecular weight component contained in the silicone-modified resin constituting the back layer migrates to the heat-meltable ink layer. The portion of the ink layer to which the low molecular weight component has migrated does not transfer to a receptor because of poor adhesion to the receptor. In addition to such a transfer disturbance, there is a further problem that the migration of a component of the ink layer to the back layer invites a decrease in the slipping property of the back layer, resulting in a disturbance of the travelling of the thermal transfer recording medium.
In view of the foregoing, an object of the present invention is to provide a thermal transfer recording medium which is free from the transfer disturbance and travelling disturbance due to the migration of a component of the back layer thereof to the ink layer thereof the and migration of a component of the ink layer to the back layer.
This and other objects of the present invention will become apparent from the description hereinafter.